A coil to be used for a large power generator includes a coil conductor and coil insulation layers, which coat the coil conductor. The coil is manufactured by winding an insulation tape around the coil conductor, impregnating the insulation tape with an insulation resin of a low viscosity liquid state under a reduced pressure, and heating and curing the resin while press-molding the resin into a preset cross-sectional shape. When the large power generator coil is manufactured and a resin unimpregnated portion is generated in a resin impregnation process, insulation breakdown is concerned to occur from this unimpregnated portion.
It is required to sufficiently increase a time of the resin impregnation process to prevent the resin unimpregnated portion from being generated. However, when the time is increased more than necessary, productivity of coils is lowered. Therefore, the time is desired to be a minimum required time. A method for finishing the resin impregnation process within the sufficient and minimum required time includes two types of methods, namely, a method of predicting in advance a time required for resin filling, and a method of directly detecting resin filling.
According to the method of predicting a time required for resin filling, by performing precise numerical analysis and analyzing a resin impregnation flow, it is possible to predict a time at which the resin filling is finished. However, depending on a composition of the insulation tape and a condition during molding of an actual coil, a time at which the resin impregnation process is finished varies. Depending on the degree of variation, a time longer than the time predicted by the analysis may be required. When a difference between resin impregnation process finish times predicted by analysis and taken by actual molding is taken into account and a certain extended time is added to a predicted time of an analysis result, it is possible to prevent the resin unimpregnated portion from being generated by a variation in the resin impregnation process finish time. However, the extended time lowers productivity. It is conceivable that a suitable method for finishing the resin impregnation process within a minimum required time while preventing the resin unimpregnated portion from being generated by the variation is the method of directly detecting resin filling.
Conceivable means for detecting an arrival of a liquid to a specific position is firstly a method of visually observing the liquid. Impregnation with a resin takes place from an outer side to an inner side of a coil. Therefore, an innermost layer of an insulation layer is lastly filled with the resin. However, it is difficult to visually observe from the outside that the innermost layer is filled with the resin. Therefore, it is required to use a device capable of detecting resin impregnation to directly detect the resin filling.
Characteristics required for the resin impregnation detection device are the capability of accurately detecting resin impregnation, and a small size that allows the resin impregnation detection device to be installed in a narrow portion. The insulation layer before the resin impregnation is in a state in which an insulation tape is wound around a coil conductor, and the innermost layer is an extremely small region in which the coil conductor and the insulation tape are substantially in contact with each other. The resin impregnation detection device is required to be small to allow the resin impregnation detection device to be installed in the extremely small region between layers of the insulation tape and between the coil conductor and the insulation tape.
As a small detection device, there is given an optical fiber. The optical fiber includes a core at a center portion, and a clad, which covers the core. The optical fiber traps light in the core and propagates the light by reflecting the light on an interface between the core and the clad. The optical fiber has a thin outer diameter of approximately several hundreds of micrometers, and can be inserted even in a narrow portion between the coil conductor and the insulation tape.
Such a resin impregnation detection device including an optical fiber is, for example, a resin impregnation detection device including: an optical fiber; a coating resin layer, which coats the optical fiber; and a linear elastic body, which is disposed in parallel to the optical fiber under a state in which a tension is applied to an interior of the coating resin layer or an outer side of the coating resin layer (see, for example, Patent Literature 1). The coating resin layer is formed of a resin whose strength is to be lowered by contact with an impregnated resin being a detection target liquid. When the strength of the coating resin layer is lowered by the contact with the impregnated resin, the tension of the linear elastic body bends the optical fiber. When the optical fiber is bent, light leaks from the bent portion to an outside of the core, and optical loss occurs. Consequently, through measurement of this optical loss, it is possible to detect the resin impregnation.